Quantitative analysis using solids inlet probe are being done in 4 areas: (1) Calcium isotope ratios by thermal ionization for studies of calcium kinetics; (2) Disaturated lecithins as an asaay for a potential independent risk factor in atherosclerosis; (3) 13C labeled amino acids for use as tracers in metabolic studies; (4) Melatonin as a methodologically independent validation for melatonin RIA results. Multivariate statistical methods are being applied to large mass spectral data sets. Mathematical modeling studies of quadrupole mass spectrometers are being conducted. The physiologic role and regulation of the pineal hormone melatonin is being studied in human subjects and animals. Plasma melatonin is being studied in obese children, in precociously pubescent children, and in women with breast cancer. Pineal melatonin is being measured in rodents to investigate the circadian regulation of this hormonal and its ontogeny. Estrogen and progesterone receptors are being measured in hamster uteri to study the effect of acute melatonin treatment on these receptors. The inhibitory effect of melatonin on the induction of mammary tumors in dimethylbenzathracene treated rats is being studied. In vitro production of melatonin by a single chicken pineal gland is being studied.